JP2001257423A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser which suppresses deterioration nearby its end surface by an easy method and then has high reliability even in high-output operation. SOLUTION: This semiconductor laser has a 1st conductivity semiconductor substrate, an ohmic electrode for the 1st conduction which is formed in contact with one surface of the substrate, at least a 1st conductivity clad layer which is formed on the reverse surface of the substrate, an active layer, an epitaxial layer which includes a 2nd conductivity clad layer and a 2nd conductivity contact layer, and an ohmic electrode for the 2nd conductivity which is formed on the contact layer for the 2nd conductivity in contact. The ohmic electrode for the 1st conductivity is not in contact with the 1st conductivity substrate on at least one laser end surface, and the ohmic electrode for the 2nd conductivity is not in contact with the 2nd type contact layer on at least one layer and surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser. The semiconductor laser of the present invention is suitably used particularly for applications requiring high output and long life, such as an excitation light source for an optical fiber amplifier.

[0002]

2. Description of the Related Art The progress of optical information processing technology and optical communication technology in recent years has been remarkable. For example, there is no shortage of high-density recording using a magneto-optical disk and two-way communication using an optical fiber network. In the telecommunications field in particular, along with a large-capacity optical fiber transmission line that is fully compatible with the future of the multimedia era, an optical fiber doped with a rare earth element such as Er ^{3+ is used} as an amplifier for signal amplification with flexibility for the transmission system. Research on amplifiers (EDFA) has been actively conducted in various fields. The development of a high-power, long-life semiconductor laser, which is an indispensable component of an EDFA, has been awaited.

[0003] In principle, there are three types of oscillation wavelengths of semiconductor lasers that can be used for EDFA applications.
m, 980 nm and 1480 nm. From the viewpoint of the amplifier itself, the excitation at 980 nm is the gain,
It is known that noise and the like are most desirable. Since this laser having an oscillation wavelength of 980 nm is used by being coupled to an optical fiber, the emitted laser light must have a stable transverse mode regardless of injection current, temperature, return light from the fiber end face, and the like. desired.
Furthermore, since it is an excitation light source, high output and long life are also expected. Further, there is a demand for an SHG light source at a wavelength in the vicinity of this, and the development of a high-performance laser in various other application fields is awaited.

[0004] However, the previously reported 980
High-power semiconductor lasers with wavelengths around nm, especially
In a laser which is an excitation light source of the EDFA as described above and operates on a single transverse mode, deterioration near an end face thereof is a serious problem. This is one of the reasons that the emission end face of the laser light is exposed to a very high light density. As is well known in GaAs / AlGaAs-based semiconductor lasers, there are many surface levels near the end face, and these levels act as non-radiative recombination centers. For this reason, light absorbed near the end surface causes heat generation in the vicinity. Therefore, generally, the temperature near the end face is higher than the temperature inside the laser. Further, it is described that this temperature rise causes positive feedback such that the band gap near the end face is narrowed and laser light is more easily absorbed. This phenomenon is the so-called COD (Catastro
phicOptical Damage), and sudden deterioration of the device due to a decrease in COD level during a long-term current test,
Or it is observed as sudden death.

[0005] In order to solve these problems, various proposals have been made so far. For example, there is a method of epitaxially growing a semiconductor material transparent to an oscillation wavelength on a laser end face to reduce light absorption near the end face. However, in this method, since the laser is grown in a so-called bar state and epitaxial growth is performed on the end face, the subsequent electrode process becomes very complicated.

Various methods have also been proposed for disordering the active layer by intentionally diffusing Zn or Si or the like as impurities into the active layer in the vicinity of the end face of the laser as heat diffusion or ion implantation (Japanese Patent Laid-Open No. 2-59992). JP, JP-A-3-31083, JP-A-6-3029
06 publication). However, the impurity diffusion generally performed in the LD manufacturing process is the first in the epitaxial direction of the laser device.
Since it is performed in the direction of the conductive type substrate, there is a problem in controlling the diffusion depth and in controlling the diffusion in an unintended direction such as the direction of the resonator, so that stable fabrication is difficult. Also, in the case of ion implantation, high-energy ions are introduced from the end face, so that even if an annealing process is performed, damage tends to remain on the LD end face. In addition, an increase in reactive current due to a decrease in resistance in a region into which impurities are introduced has a problem that a threshold current and a drive current of a laser increase. As described above, none of the semiconductor light emitting devices proposed so far and the manufacturing method thereof have been technically satisfactory.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems of the prior art. That is, an object of the present invention is to provide a semiconductor laser in which deterioration near the end face of a semiconductor laser is suppressed by a simple method and, as a result, high reliability is ensured even during high-power operation.

[0008]

The inventor of the present invention has made intensive studies to solve these problems, and as a result, a first conductive type semiconductor substrate and a first conductive type semiconductor substrate formed on one surface of the substrate. An ohmic electrode for conductivity type, an epitaxial layer including at least a first conductivity type clad layer, an active layer, a second conductivity type clad layer and a second conductivity type contact layer formed on the opposite surface of the substrate; A semiconductor laser having an ohmic electrode for a second conductivity type formed so as to be in contact with a contact layer for a second conductivity type, wherein the ohmic electrode for the first conductivity type is provided on at least one laser end face.
The problem is solved by the semiconductor laser of the present invention, wherein the semiconductor laser is not in contact with the conductive type substrate, and the second conductive type ohmic electrode is not in contact with the second conductive type contact layer on at least one laser end face. We found that it could be solved.

In the semiconductor laser of the present invention, the distance between the region where the ohmic electrode for the first conductivity type is in contact with the substrate of the first conductivity type and the laser end face is Rn (μm), and the ohmic electrode for the second conductivity type is Rn (μm). Is Rp (μm), the cavity length of the semiconductor laser is Lc (μm), and the thickness of the first conductivity type cladding layer is T _clad1 ( μm), the thickness of the second conductivity type cladding layer is T _clad2 (μm), and the thickness of the second conductivity type contact layer is T _cont2 (μm). It is preferable to satisfy the conditions.

Rp ≦ Rn (Formula 1) 0.02 × Lc ≦ Rp (Formula 2) 5 × (T _clad2 + T _cont2 ) ≦ Rp (Formula 3) 20 × T _clad1 ≦ Rn (Formula 4)

As a preferred embodiment of the semiconductor laser of the present invention, preferably, the entire surface of the first conductivity type semiconductor substrate on which the first conductivity type ohmic electrode is not formed is formed.
An embodiment in which the first Schottky electrode is formed so as to be in contact therewith; a current confinement layer (preferably Si) having an opening between the second conductivity type contact layer and the second conductivity type ohmic electrode.
Nx, SiOx or AlOx dielectric film) is formed, and the second conductivity type contact layer and the second conductivity type ohmic electrode are in contact at the opening; the first conductivity type is n-type; An embodiment in which the second conductivity type is p-type; an embodiment in which the active layer includes a quantum well structure;
Embodiment in which the thickness is 100 to 1200 nm; the substrate is a GaAs first conductivity type substrate, and the active layer is undoped In _x Ga _{1 -x.}
An embodiment including an As (0 <x <1) strained quantum well and having an optical guide layer; an n-type impurity, preferably Si, in the optical guide layer
And an embodiment in which the light guide layer is GaAs.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a preferred configuration example of a semiconductor laser of the present invention and a method of manufacturing the same will be specifically described. A semiconductor laser of the present invention includes a first conductivity type semiconductor substrate, a first conductivity type ohmic electrode formed so as to be in contact with one surface of the substrate, and at least a first conductivity type ohmic electrode formed on an opposite surface of the substrate. 1 conductivity type cladding layer, active layer, 2nd
At least an epitaxial layer including a conductive type cladding layer and a second conductive type contact layer, and a second conductive type ohmic electrode formed so as to be in contact with the second conductive type contact layer. The features of the semiconductor laser of the present invention are:
The point lies in that both of the above Rn and Rp are not 0 on at least one end face.

The structural features of the semiconductor laser according to the present invention will be described with reference to specific embodiments of the present invention shown in FIGS. In this embodiment of the semiconductor laser, as shown in the sectional view of FIG. 2, the semiconductor wafer has a refractive index waveguide structure, the second conductivity type clad layer is divided into two layers,
A lateral light confinement structure is formed by the conductive type second cladding layer and the current blocking layer. Specifically, a buffer layer (2), a first conductive type clad layer (3), an active layer (4), and a second conductive type first clad layer (5) are formed on a first conductive type semiconductor substrate (1). ), A second etching stopper layer (6), a first etching stopper layer (7), a current blocking layer (9), and a cap layer (10) are formed in this order. Layer (9), cap layer (1
In (0), an opening to be a current injection region (13) is formed by etching. The opening and the cap layer (1
A second conductive type second cladding layer (8) and a second conductive type contact layer (11) are formed on 0). On the second conductivity type contact layer (11), a current confinement layer (21) having an opening (14) opening from the end face to the inside by Rp is formed as shown in FIG. An ohmic electrode (22) for the second conductivity type is formed inside the opening (14) and on the current confinement layer (21). Also,
On the opposite side of the substrate (1), as shown in FIG.
The first conductivity type ohmic electrode (3
1) and a first Schottky electrode (32) formed so as to cover the entire surface of the electrode.

In the semiconductor laser of the present invention, a single-crystal substrate such as GaAs or InP is often used as the first conductivity type semiconductor substrate (1). Most often G
An aAs first conductivity type substrate is used. The first conductivity type semiconductor substrate (1) made of these single crystals is usually obtained by cutting out from a bulk crystal.

The buffer layer (2) is preferably provided to alleviate the incompleteness of the bulk crystal of the first conductivity type substrate and facilitate the formation of an epitaxial thin film having the same crystal axis. The buffer layer (2) is preferably composed of the same compound as the first conductivity type semiconductor substrate (1).
GaAs is used. The buffer layer need not necessarily be formed.

The first conductivity type cladding layer (3) is usually made of a material having a refractive index smaller than that of the active layer (4), and when GaAs is used as the buffer layer (2), AlGaAs-based material (Al _V Ga _1-V As)
Is used, and the mixed crystal ratio is appropriately selected so that the refractive index satisfies the above condition.

The material and structure of the active layer (4) are appropriately selected according to the desired oscillation wavelength and output, and any material or structure can be used. However, the active layer used in the present invention preferably includes a quantum well structure. Band gap reduction effect (S.Tarucha
et al., Jpn. J. Appl. Phys. vol 23, pp. 874-878,19
84), it is widely known that generally the oscillation of a semiconductor laser occurs on the longer wavelength side than the spontaneous emission light of the active layer. The active layer including the quantum well has a feature that the absorption on the long-wavelength side where oscillation oscillates is much smaller than that of the bulk active layer, reflecting the stepwise state density. For this reason, as described later, when the ohmic electrodes for the first conductivity type and the second conductivity type are separated from the end face by an appropriate distance to suppress current injection near the end face, the active layer including the quantum well is used. In comparison with the bulk active layer, there is an advantage that the absorption of the portion where the current injection is suppressed as a waveguide can be reduced.

Further, the active layer is an undoped In _x Ga _{1 -x} As (0 <x <) formed on a GaAs first conductivity type substrate.
1) It is desirable to include a strained quantum well. In this system, a compressive stress is applied to the active layer, and if it does not exceed the critical film thickness, there is a possibility that the absorption of the portion where the current injection is suppressed as the waveguide can be further reduced. This is particularly effective for a laser having an oscillation wavelength of about 900 to 1200 nm.

As the structure of the active layer, various structures (SQW-sing
le quantum well, MQW-multi quantum well) and the like. When a quantum well is included, an optical guide layer is usually used together. As a structure of the light guide layer, a structure in which light guide layers are provided on both sides of the active layer (SCH structure), and a structure in which the refractive index is continuously changed by gradually changing the composition of the light guide layer (GRIN- (SCH structure) or the like. The composition of the light guide layer is preferably Al _x Ga _{1 -x} As (0 ≦ x ≦ 1), and more preferably GaAs.

It is preferable that the light guide layer contains an n-type impurity. This reduces the electrical resistance of the active layer as a whole, and when carriers are injected into the active layer, extreme diffusion of carriers from the current injection end of each ohmic electrode to the laser end face is promoted, or current injection near the end face is performed. This is effective in preventing the suppression effect from being impaired.

The second conductive type first cladding layer (5) is made of a material having a smaller refractive index than the active layer (4).
And the refractive index of the second conductivity type first cladding layer (5);
The refractive index of the first conductivity type cladding layer (3) is usually the same. Accordingly, the material of the second conductivity type first cladding layer (5) is usually the same as that of the first conductivity type cladding layer (3).
An AlGaAs-based material is used, and its mixed crystal ratio is usually the same as that of the first conductivity type cladding layer (3). In this structure, the second conductive type first cladding layer (5) is, Al _W Ga _1-W
This corresponds to a layer made of As.

FIG. 1 shows two types of etching stopper layers and
And cap layers are described, but these layers
In a preferred embodiment, the current injection region
This is effective for performing the insertion precisely and easily. Second edge
The tinning prevention layer (6) is made of Al _aGa_1-aAs (0 ≦ a ≦
1) Made of material, but GaAs is usually preferred
Is done. This is the second conductivity type second crack by MOCVD or the like.
Layer, etc., especially when regrown with an AlGaAs system.
This is because the layers can be stacked with good crystallinity. 2nd etch
The thickness of the blocking layer (6) is usually preferably 2 nm or more.

The first etching stop layer (7) is made of In _b G
A layer represented by a _1-b P (0 ≦ b ≦ 1) is preferable. When GaAs is used as the first conductivity type semiconductor substrate as in the present invention, b = 0 in a system having no distortion. .5 are used. The thickness of the first etching stop layer is usually 5 nm or more, preferably 10 nm or more. In addition, In _0.5 G
a _0.5 P is inferior in heat dissipation to AlGaAs,
00 nm or less is preferable. If the thickness is less than 5 nm, etching may not be able to be stopped due to a disorder of the film thickness or the like. On the other hand, depending on the film thickness, a strain system can be used, and b = 0, b = 1, and the like can be used. When a strain system is used, the film thickness is from one molecular layer to one.
It is 5 nm, preferably 10 nm or less. If the film thickness is thin in such a manner, there is no problem even if lattice matching cannot be attained because the intrinsic strain is alleviated.

The current blocking layer (9) is a layer having a function of literally blocking a current and substantially not flowing the current.
For this reason, the conductivity type of the current blocking layer is preferably the same as or undoped from the first conductivity type cladding layer, and the second conductivity type is usually made of Al _y Ga _1-y As (0 <y ≦ 1). It is preferable that the refractive index is smaller than that of the second cladding layer (8). Normally, the current blocking layer is also made of Al _z Ga _1-z
As (0 ≦ z ≦ 1) is preferable, and therefore it is preferable that the mixed crystal ratio satisfies z ≧ y. Also,
In relation to the above-described light guide layer, it is preferable that x <y ≦ z.

The current blocking layer is made of In _0.5 Ga _0.5 P
Can also be configured. In that case, Al _a Ga _1-a As
(0 ≦ a ≦ 1) In only the second etching stopper layer (6)
The etching of the _0.5 Ga _0.5 P current blocking layer can be stopped, and the subsequent Al _y Ga _1-y As (0 <y ≦
1) can be performed easily even regrowth of the second conductivity type second cladding layer (8), above _{In b Ga 1-b P (} 0 ≦ b
The first etching stop layer (7) of ≦ 1) is unnecessary.

The current injection region (13) formed by the current block layer is preferably opposed to the region where the ohmic electrode for the first conductivity type is in contact with the substrate of the first conductivity type. Further, the current injection region (13) formed by the current blocking layer is preferably opposed to a region where the ohmic electrode for the second conductivity type is in contact with the contact layer for the second conductivity type.

In order to realize a semiconductor laser having a longer life, the first cladding layer (3) of the first conductivity type and the first
For the cladding layer (5), the second conductivity type second cladding layer (8), and the like, it is preferable to use a material having a not too high Al mixed crystal ratio. Specifically, the Al mixed crystal ratios v, w, and y of each layer
Is preferably 0.4 or less.
More preferably, 0.3-from the relationship with the laser temperature characteristics
Set within the range of 0.4.

The cap layer (10) is used as a protective layer of the first current blocking layer (9) in the first growth and at the same time facilitates the growth of the second conductivity type second cladding layer (8). Used and removed partially or completely before obtaining the device structure.

The second conductive type second cladding layer (8) is made of a material having a smaller refractive index than the active layer (4).
The refractive index of the second-conductivity-type second cladding layer (8) is determined by the first-conduction-type cladding layer (3) or the second-conduction-type first cladding layer (5).
Is usually the same as the refractive index. Therefore, the second conductivity type second
The material of the cladding layer (8) is usually AlGaAs
A base material is used, and its mixed crystal ratio is usually the same as the first conductivity type clad layer (3) and the second conductivity type first clad layer (5).

On the second conductive type second cladding layer (8), a second conductive type contact layer (11) is provided for the purpose of lowering the contact resistivity of the electrode. The second conductivity type contact layer (11) is usually made of a GaAs material. This layer usually has a higher carrier concentration than the other layers in order to lower the contact resistivity with the electrode.

The thickness of each layer constituting the semiconductor laser of the present invention is not particularly limited as long as it can effectively perform the functions required for each layer. Usually, the thickness of the buffer layer (2) is 0.1 to 1 μm, preferably 0.5 to 1 μm,
The thickness of the conductive type cladding layer (3) is 0.5 to 5 μm, preferably 1 to 3 μm, and the thickness of the active layer (4) is 0.0005 to 0.02 μm, preferably 0.1 μm per layer in the case of a quantum well structure. 003 to 0.2 μm, the thickness of the second conductivity type first cladding layer (5) is 0.05 to 0.3 μm, preferably 0.05 to 0.2 μm, and the thickness of the second conductivity type second cladding layer (8). The thickness is 0.5-5 μm, preferably 1-3 μm
m, the thickness of the cap layer (10) is 0.005 to 0.5 μm
m, preferably 0.005 to 0.3 μm, and the thickness of the first conductivity type current blocking layer (9) is selected from the range of 0.3 to 2 μm, preferably 0.3 to 1 μm.

It is desirable to provide a current confinement layer (21) on the second conductivity type contact layer (11). This layer reduces the area where the second conductive type ohmic electrode (22) is in direct contact with the second conductive type contact layer (11), and injects the second conductive type carrier into the cavity of the laser chip. Alternatively, it is formed to limit in a direction perpendicular to this. The material of the current confinement layer (21) is not limited as long as it does not allow a current to flow.
It is desirable that the dielectric material contains iNx, SiOx, and AlOx. Of these, SiNx is particularly preferred. The thickness of such a dielectric film is preferably 500 nm or less, more preferably 250 nm or less, and 1 nm or less.
It is particularly preferred that it is 50 nm or less.

The current confinement layer (21) is provided with a current injection path for allowing a second conductivity type ohmic electrode (22) to be described later to contact the second conductivity type contact layer (11). Become. Such a current injection path is formed, for example, by forming a current confinement layer (21) on the entire surface of the second conductivity type contact layer (11), removing only a current injection region by a photolithography method or the like, and forming a second layer from the top. The two-conductivity type ohmic electrode (22) can be easily formed by a method such as vapor deposition of an electrode.

The second conductivity type contact layer (11) is in direct contact with, or part of, the current confinement layer (21).
, An ohmic electrode (22) for the second conductivity type is formed. A region where the second conductive type ohmic electrode (22) is in direct contact with the second conductive type contact layer (11) is formed at a distance of Rp (μm) from at least one laser end face. This portion has a function of preventing injection of carriers of the second conductivity type into the laser. Therefore, when the laser is operating at a high output or at a high temperature, the current load near the end face is reduced, thereby deteriorating the laser. It is effective in suppressing

When the ohmic electrode for the second conductivity type is formed in direct contact with the contact layer (11) for the second conductivity type, the portion where the current is not injected is the ohmic electrode for the second conductivity type. This can be realized by forming the electrode itself at a distance Rp (μm) from at least one end face. On the other hand, when a part of the second conductive type ohmic electrode (22) is in contact with the second conductive type contact layer (11) via the current confinement layer (21), a current injection path is formed. At this time, it can be realized by separating the injection path by at least Rp (μm) from one laser end face. In particular, the effect of not injecting a current to the front end face side where a large amount of laser light is emitted is great. In general, the second conductive type contact layer (11) and the second conductive type ohmic electrode (22) are brought into contact with each other on both sides of the end face forming the resonator by a distance Rp (μm). desirable.

The material of the ohmic electrode (22) for the second conductivity type is not limited, but when the second conductivity type is p-type, an electrode composed of each layer of Ti / Pt / Au from the contact layer side, or An electrode composed of each layer of AuZn / Au is desirable. Also, when the second conductivity type is n-type, Ti
An electrode composed of each layer of / Pt / Au can be used. Generally, these electrodes are alloyed to achieve ohmic contact with the second conductivity type contact layer (11).

The first conductive type ohmic electrode (31) is formed on the first conductive type semiconductor substrate (1) at a distance of Rn (μm) from at least one laser end face. This portion has a function of preventing injection of the first conductivity type carrier into the laser, and is therefore effective in suppressing the deterioration of the end face when the laser performs a high-power operation. This effect functions more effectively in combination with the fact that carriers are not injected from the second conductive type ohmic electrode (22) into the vicinity of the end face, and is important for ensuring high power operation and reliability during high temperature operation of the laser. Will play an important role.

The ohmic electrode (31) for the first conductivity type is not particularly limited in its material and the like. For example, when an n-type is assumed as the first conductivity type, AuGe / Ni / Au is sequentially deposited. And those formed by alloying are desirable. When a p-type is assumed, Ti / Pu / A
It is desirable that the substrate be formed by successively depositing u and then performing an alloying process. In this case, AuZn /
It is also desirable that Au be sequentially deposited and then formed by alloying.

On the substrate on which the first conductive type ohmic electrode (31) is formed, the first conductive type ohmic electrode (3) is formed.
Preferably, a first Schottky electrode (32) is formed so as to cover 1). This is because when the substrate side is mounted on a heat radiating plate such as AlN using a solder material such as AuSn, the first Schottky electrode ensures the function of preventing current from being injected near the end face and the heat radiation property near the end face. This is for realizing the compatibility of the functions to be performed. The first Schottky electrode (31) is not limited as long as it has a Schottky characteristic with respect to the first conductivity type substrate.
It is desirable that Au or the like be sequentially deposited.

In the semiconductor laser of the present invention, the distance Rp
(Μm) and Rn (μm) preferably satisfy the condition of the above (Equation 1). This is because the thickness of the first conductivity type semiconductor substrate (1) is generally thicker than that of the second conductivity type contact layer (11) and the like. Diffusion of carriers from the injection end to the end face side can be effectively reduced.

Further, in the semiconductor laser of the present invention, it is preferable that the conditions of the above-mentioned (Equation 2) to (Equation 4) are also satisfied. By satisfying these conditions, current injection to the vicinity of the laser end face can be more effectively suppressed. This comprises a first conductivity type cladding layer (3), an active layer (4), a second conductivity type first layer.
Cladding layer (5), second conductivity type second cladding layer (8),
This is because, even if the injected carriers diffuse in the second conductivity type contact layer (11) and the like, the effect of suppressing the current injection is preserved near the end face. Note that Rn and R
As for p, it is preferable that both end faces satisfy the conditions of (Equation 1) to (Equation 4).

A wafer completed by forming electrodes thereon is first cleaved by a laser bar. The end face of the laser bar is usually asymmetrically coated with Si, Al ₂ O ₃ , SiN _x or the like so that the front end face reflectivity is about 2.5% and the rear end face reflectivity is about 93%. It is divided and used as a laser diode (LD). Although the above description relates to a groove type semiconductor laser, the present invention can be similarly applied to a ridge type semiconductor laser as long as the effective refractive index difference is within the range described in the claims.

The method of manufacturing the basic epitaxial structure and the method of manufacturing devices of various semiconductor lasers including the embodiments shown in FIGS. 1 and 2 are not particularly limited. For example, a method for manufacturing an epitaxial structure is disclosed in Japanese Patent Application Laid-Open No. 8-13034.
No. 4 can be referred to.

The semiconductor laser of the present invention is used as a light source for an optical fiber amplifier used for optical communication and as a pickup light source for a large-scale magneto-optical memory for information processing. It can be applied to various uses.

[0044]

The present invention will be described more specifically with reference to the following examples. Materials, concentrations, thicknesses, operation procedures, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown in the following examples. In FIGS. 2 and 3 referred to in the following embodiments, there are portions where the dimensions are intentionally changed in order to facilitate understanding of the structure, but the actual dimensions are as described in the following embodiments. It is.

(Embodiment 1) In this embodiment, FIGS.
By forming each layer in the order shown in (g), a groove type laser element was manufactured. The layer configuration of the laser device manufactured in this example is as shown in FIG. 2 showing a section taken along the line AA ′ in FIG.

Carrier concentration 1 × 10¹⁸cm^-3N-type Ga
A buffer is formed on the As first conductivity type substrate (1) by the MBE method.
The carrier layer (2) is 1 μm thick and has a carrier concentration of 1 × 10¹⁸
cm ^-3N-type GaAs layer, first conductivity type cladding layer (3)
2.5 μm thickness and carrier concentration of 1 × 10¹⁸cm^-3
N-type Al_0.35Ga_0.65Thick as As layer and active layer (4)
Carrier concentration 1 × 10 at 30 nm¹⁷cm^-3Si Do?
GaAs light guide layer, 6 nm thick undoped In
_0.16Ga_0.84As strained quantum well layer with 10 nm thickness
A concentration 1 × 10¹⁷cm^-3Si Do? GaAs barrier
Layer, 6 nm thick undoped In_0.16Ga_0.84As distortion
Sub well layer and carrier concentration of 1 × 10 at 30 nm thickness
¹⁷cm^-3Si Do? GaAs light guide layer
The second conductive type first clad layer (5) has a thickness of 0.1
Carrier concentration 1 × 10 at μm¹⁸cm^-3P-type Al_0.35G
a_0.65Thickness as As layer and second etching stop layer (6)
Carrier concentration 1 × 10 at 10 nm¹⁸cm^-3P-type GaAs
s layer, thickness 20 nm as first etching stop layer (7)
5 × 10 carrier concentration¹⁷cm^-3N-type In_0.49Ga
_0.510.5 μm thickness as P layer and current block layer (9)
5 × 10 carrier concentration¹⁷cm^-3N-type Al_0.39Ga
_0.61As layer and cap layer (10) with a thickness of 10 nm
Carrier concentration 1 × 10¹⁸cm^-3N-type GaAs layers
Laminated.

Next, a width of 1.5 on the cap layer (10).
A SiN mask having a μm stripe-shaped opening was provided. Etching is performed using the first etching stop layer (7) as an etching stop layer, and a cap layer (10) and a current blocking layer (9) to form a current injection region (13).
Was removed. At this time, sulfuric acid (98
% By mass), hydrogen peroxide (30% by mass aqueous solution) and water mixed at a volume ratio of 1: 1: 5.
Etching was performed for seconds.

Next, HF (49%) and NH ₄ F (40
%) In an etching solution mixed at a ratio of 1: 6 for 2 minutes and 30 seconds to remove the SiN layer, and further, the second etching stopper layer was used as an etching stop layer to remove the first etching stopper layer in the current injection region by etching. (FIG. 3 (a)). At this time, a mixture of hydrochloric acid (35% by mass) and water at a ratio of 2: 1 was used as an etching solution, and etching was performed at 25 ° C. for 2 minutes.

Thereafter, a carrier concentration of 1 × 10 ¹⁸ cm is formed as a second conductive type second clad layer (8) by MOCVD.
^-3 p-type Al _0.35 Ga _0.65 As layer is grown so that the thickness of the current injection region (13) becomes 2.5 μm, and a second conductivity type contact thereon for maintaining good contact with the electrode. As a layer (11), a p-type GaAs layer having a thickness of 3.5 μm and a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ is grown,
The laser epitaxial layer (12) was completed (FIG.
(B)).

Further, a 125 nm SiN film was formed on the second conductive type contact layer (11) of the formed wafer by a plasma CVD method. Next, an opening (14) was formed in the SiN film using a photolithography technique and a normal etching technique to form a current confinement layer (21). The opening (14) was formed so as to be located immediately above the current injection region (13) sandwiched between the current blocking layers (9) (FIG. 3 (c)). The opening width in the direction perpendicular to the resonator direction is 2
5 μm and 60 μm from both resonator end faces formed an area where no current was injected without forming an opening. SiN
Was performed using SF ₆ plasma.

Further, the opening (14) and the current confinement layer (2)
On top of 1), a Ti / Pt / Au electrode was formed using normal photolithography technology and a lift-off method, and patterned. The film thickness at this time is 70 nm / 70, respectively.
nm / 700 nm. Thereafter, heat treatment was performed at 450 ° C. for 10 minutes to form a p-type ohmic electrode as the second conductive type ohmic electrode (22) (FIG. 3D). The formed electrode was protected with a photoresist, and the n-type GaAs first conductivity type substrate (1) was polished so that the entire wafer had a thickness of 120 μm.

After cleaning the wafer, the current injection region (1) is formed by using a usual photolithography technique and a lift-off method.
An AuGe / Ni / Au electrode is deposited at a thickness of 100 nm / 20 nm / 500 nm so as to be located immediately below 3),
Patterned. At this time, the width in the direction perpendicular to the resonator direction is 100 μm, and 60 μm from both resonator end faces.
m is such that a region into which no current is injected is formed.
Thereafter, the entire wafer was heat-treated at 400 ° C. for 5 minutes to form an n-side ohmic electrode as the first conductivity type ohmic electrode (31) (FIG. 3E). Finally, a Ti / Au first Schottky electrode (32) is placed on the n-side of the wafer for 1
Vapor deposition was performed on the entire surface of 0 nm / 500 nm to complete a semiconductor laser wafer (FIG. 3F).

Thereafter, the wafer was set to a cavity length of 1000 μm.
m, and asymmetrical coating is applied to the end face according to a conventional method so that the front end face reflectivity is 2.5% and the rear end face reflectivity is 95%. It was divided into 500 μm chips to make a single laser element. Further, the substrate side of these devices is
The device was completed by bonding to the N submount using AuSn solder and applying wire bonding for current injection and the like.

The semiconductor laser manufactured in the present embodiment has the Rp
Is 60 μm, Rn is 60 μm, and the cavity length Lc is 1000
μm, the thickness T _clad1 of the n-side cladding layer is 2.5 μm, p
The thickness T _clad2 of the side cladding layer is 2.6 μm (2.5+
0.1), the thickness T _cont2 of the p-side contact layer is 3.5 μm
m, all the conditions of the above (Equation 1) to (Equation 4) are satisfied.

FIG. 4 shows the current light output characteristics of the device manufactured in this example at the time of CW driving at room temperature. The threshold current was 20.6 mA, and the slope efficiency was 0.87 W / A. The maximum light output specified by the thermal saturation was 636.8 mW, and no COD deterioration or the like due to the destruction of the end face was observed until the current injection of 2 A. Further, 350 was performed to check the reliability of the element.
As a result of testing the life of five devices in an environment of 50 ° C. at an mW output, no device suddenly died during the test up to 1000 hours, and the standardized deterioration rate was 9.0 × 10 ⁻⁶ (1/1).
h), and a very stable operation was confirmed.

(Example 2) With the exception that the current confinement layer (21) is not formed, the Ti / Pt / Au electrode as the second conductivity type ohmic electrode is formed directly on the p-type contact layer side. A device was manufactured in the same manner as in Example 1.
At this time, the opening width of the Ti / Pt / Au electrode in the direction perpendicular to the resonator immediately above the current injection region is 400 μm by using a normal photolithography technique and a lift-off method.
And processing was performed such that a region into which current was not injected was formed at 50 μm from both resonator end faces.

The current light output characteristics of the fabricated device during CW driving at room temperature were examined.
0.4 mA, and the slope efficiency was 0.86 W / A. The maximum light output defined by thermal saturation is 61
It was 5.4 mW, and no COD deterioration or the like due to the destruction of the end face was observed until the current injection of 2 A. In order to examine the reliability of the device, the life of five devices was tested in an environment of 50 ° C. at an output of 350 mW. As a result, none of the devices suddenly died during the test up to 1000 hours, and the standardized deterioration rate was 9%. 0.5 × 10 ⁻⁶ (1 / h), indicating a very stable operation.

Example 3 A device was manufactured in the same manner as in Example 1 except that the formation of the first Schottky electrode (32) after forming the first conductivity type ohmic electrode was omitted. When the current light output characteristics of the fabricated device during CW driving at room temperature were examined, the threshold current was 20.8.
mA and the slope efficiency was 0.85 W / A.
The maximum light output defined by thermal saturation is 595.3.
mW, and no COD degradation or the like due to destruction of the end face was observed until the current injection of 2 A. In order to examine the reliability of the device, the life of five devices was tested in an environment of 350 mW output and 50 ° C. As a result, none of the devices suddenly died during the test up to 1000 hours, and the standardized deterioration rate was 1 .0x10 a ^-5 (1 / h), stable operation was confirmed.

(Example 4) The current confinement layer (21) is formed so that the width of the opening (14) in the direction perpendicular to the resonator direction is 30 μm.
Then, 10 μm from both resonator end faces is formed so as to be a region where current is not injected (Rp = 10 μm), and the first
The conductive ohmic electrode (31) was formed such that the width in the direction perpendicular to the resonator direction was 50 μm, and 15 μm from both resonator end faces was a region where current was not injected (Rn = 1).
A device was produced in the same manner as in Example 1 except that the thickness was 5 μm.

When the current light output characteristics of the fabricated device during CW driving at room temperature were examined, the threshold current was 2
0.0 mA, and the slope efficiency was 0.88 W / A. The maximum light output defined by the thermal saturation is 60
It was 0.5 mW, and no COD degradation or the like due to the destruction of the end face was observed until the current injection of 1.5 A. In order to examine the reliability of the device, the life of five devices was tested in an environment of 350 mW output and 50 ° C. As a result, none of the devices suddenly died during the test up to 1000 hours, and the standardized deterioration rate was 1 0.2 × 10 ⁻⁵ (1 / h), indicating a stable operation.

(Embodiment 5) GaAs light guide layer and GaAs
And barrier layer? A device was produced in the same manner as in Example 1 except that the device was used. When the current light output characteristics of the fabricated device at the time of CW driving at room temperature were examined, the threshold current was 24.5 mA, and the slope efficiency was 0.84 W / A. The maximum light output defined by the thermal saturation was 650.7 mW, and no COD deterioration or the like due to the destruction of the end face was observed until the current injection of 2 A. In order to check the reliability of the device, 350 mW
As a result of testing the life of the five devices in an environment of 50 ° C. at the time of output, no device suddenly died during the test up to 1000 hours, and the standardized deterioration rate was 1.3 × 10 ⁻⁵ (1 / h).
And no failure operation was confirmed.

Comparative Example 1 A second conductive type ohmic electrode was formed directly on the entire surface of the second conductive type contact layer, and a first conductive type ohmic electrode was formed directly on the entire surface of the first conductive type substrate. Produced a device in the same manner as in Example 1. FIG. 5 shows the results of examining the current light output characteristics of the fabricated device during CW driving at room temperature. The threshold current was 20.3 mA, and the slope efficiency was 0.87 W / A. The maximum light output was 528.8 mW. At this time, the device was destroyed due to COD deterioration. In order to check the reliability of the device, 50 ° C at 350 mW output
All devices were suddenly killed by 200 hours as a result of testing the life of the five elements in the same environment.

Comparative Example 2 A device was manufactured in the same manner as in Example 1 except that the first conductivity type ohmic electrode was formed directly on the entire surface of the first conductivity type substrate. When the current light output characteristics of the manufactured device at the time of CW driving at room temperature were examined, the threshold current was 20.6 mA, and the slope efficiency was 0.86 W / A. The maximum light output is 545.5
mW. At this time, the device was destroyed due to COD deterioration. To check the reliability of the device,
As a result of testing the life of five devices in an environment of 50 ° C. and 50 mW output, all devices suddenly died by 400 hours.

Comparative Example 3 A device was manufactured in the same manner as in Example 1 except that the ohmic electrode of the second conductivity type was formed directly on the entire surface of the contact layer of the second conductivity type. When the current light output characteristics of the fabricated device at the time of CW driving at room temperature were examined, the threshold current was 20.7 mA, and the slope efficiency was 0.86 W / A. Maximum light output is 5
The power was 50.7 mW. At this time, the device was destroyed due to COD deterioration. Further, in order to examine the reliability of the devices, the life of five devices was tested in an environment of 50 ° C. at a power of 350 mW, and as a result, all the devices died suddenly by 350 hours.

[0065]

According to the present invention, there is provided a semiconductor laser in which deterioration near the end face of a semiconductor laser is suppressed by a simple method, and as a result, high reliability is ensured even at a high output operation. Provide significant industrial benefits.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing one embodiment of a semiconductor laser of the present invention.

FIG. 2 is a cross-sectional view illustrating one embodiment of a semiconductor laser of the present invention.

FIG. 3 is a diagram illustrating a manufacturing process of the semiconductor laser of the present invention.

FIG. 4 is a graph showing the relationship between current and light output of the semiconductor laser of Example 1.

FIG. 5 is a graph showing the relationship between the current and the optical output of the semiconductor laser of Comparative Example 1.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate 2 Buffer layer 3 1st-conductivity-type clad layer 4 Active layer 5 2nd-conductivity-type 1st clad layer 6 2nd etching-stop layer 7 1st-etch-stop layer 8 2nd-conductivity-type 2nd clad layer 9 Current block layer 10 Cap layer 11 Second contact type contact layer 12 Epitaxial layer 13 Current injection region 14 Opening 21 Current constriction layer 22 Ohmic electrode for second conductivity type 31 Ohmic electrode for first conductivity type 32 First Schottky electrode Rn First conductivity Distance between the region where the ohmic electrode for mold is in contact with the first conductivity type substrate and the laser end surface Rp The distance between the region where the ohmic electrode for second conductivity type is in contact with the second conductivity type contact layer and the laser end surface

Claims (18)

[Claims] A first conductive type semiconductor substrate; a first conductive type ohmic electrode formed to be in contact with one surface of the substrate; and at least a first conductive type formed on an opposite surface of the substrate. Layer, an active layer, an epitaxial layer including a second conductivity type cladding layer and a second conductivity type contact layer, and an ohmic electrode for the second conductivity type formed on and in contact with the second conductivity type contact layer Wherein the first conductive type ohmic electrode is not in contact with the first conductive type substrate on at least one laser end face, and the second conductive type ohmic is provided on at least one laser end face. Wherein the conductive electrode is not in contact with the second conductivity type contact layer. 2. A distance R between a region where the first conductive type ohmic electrode is in contact with the first conductive type substrate and a laser end face.
n (μm) and a distance Rp (μm) between a region where the ohmic electrode for the second conductivity type is in contact with the second conductivity type contact layer and the laser end face satisfy the condition of Expression 1. The semiconductor laser according to claim 1, wherein Rp ≦ Rn (Equation 1) 3. The resonator length Lc (μ) of the semiconductor laser.
m) and a distance Rp (μm) between a region where the second conductive type ohmic electrode is in contact with the second conductive type contact layer and the laser end face satisfies the condition of Expression 2. Item 3. The semiconductor laser according to item 1 or 2. ## EQU2 ## 0.02 × Lc ≦ Rp (Equation 2) 4. A thickness T of the second conductivity type cladding layer.
_clad2 (μm), thickness T of the second conductivity type contact layer
_cont2 (μm) and a distance Rp (μm) between a region where the ohmic electrode for the second conductivity type is in contact with the contact layer of the second conductivity type and the laser end face satisfy the condition of Expression 3. The semiconductor laser according to claim 1. 5 x (T _clad2 + T _cont2 ) ≦ Rp (Equation 3) 5. A thickness T of the first conductivity type cladding layer.
_clad1 (μm), and the distance Rn (μm) between the laser end face and the region where the ohmic electrode for the first conductivity type is in contact with the substrate of the first conductivity type, satisfy the condition of Expression 4. The semiconductor laser according to claim 1. 20 × T _clad1 ≦ Rn (Equation 4) 6. A first Schottky electrode is formed so as to be in contact with a portion of the first conductivity type semiconductor substrate on which the first conductivity type ohmic electrode is not formed. The semiconductor laser according to claim 1. 7. A first Schottky electrode is formed so as to be in contact with the entire surface of the first conductivity type semiconductor substrate on which the first conductivity type ohmic electrode is not formed. 7. The semiconductor laser according to claim 6, wherein: 8. The second conductivity type contact layer and the second conductivity type contact layer.
A current constriction layer having an opening is formed between the conductive type ohmic electrodes, and the second conductive type contact layer and the second conductive type ohmic electrode are in contact with each other at the opening. A semiconductor laser according to claim 1. 9. The semiconductor laser according to claim 8, wherein said current confinement layer is made of a dielectric film containing SiNx, SiOx or AlOx. 10. The method according to claim 1, wherein the opening of the current confinement layer is provided in the first confining layer.
The semiconductor laser according to claim 8, wherein an ohmic electrode for conductivity type is opposed to a region in contact with the first conductivity type substrate. 11. An opening in the current confinement layer and the second
The semiconductor laser according to any one of claims 8 to 10, wherein an ohmic electrode for conductivity type is opposed to a region in contact with the second conductivity type contact layer. 12. The semiconductor device according to claim 1, wherein the first conductivity type is n-type, and the second conductivity type is p-type.
Semiconductor laser according to any of the above 13. The semiconductor laser according to claim 1, wherein said active layer has a quantum well structure. 14. An oscillation wavelength of the semiconductor laser is 900.
14. The thickness is from 1200 to 1200 nm.
The semiconductor laser according to any one of the above. 15. The GaAs substrate of the first conductivity type, wherein the active layer is undoped In _x Ga _{1 -x} As.
15. The semiconductor laser according to claim 1, comprising (0 <x <1) a strained quantum well and having an optical guide layer. 16. The semiconductor laser according to claim 15, wherein the light guide layer contains an n-type impurity. 17. The semiconductor laser according to claim 16, wherein said n-type impurity is Si. 18. The semiconductor laser according to claim 16, wherein said light guide layer is made of GaAs.